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Old 11-10-2011, 08:18 AM
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Remove CATS = Time Bomb ?

I had all three CATS removed from my WJ (2003 4.7) a few months ago. The two front CATS were replaced with straight pipes and the rear CAT was replaced with a Free Flow silencer box. (We do not yet have emission laws in South Africa)

All O2 sensors were left where they were originally in the pipes.

I have not noticed a big difference in power or fuel consumption, but she sounds soooo much better ! The engine light never came on after the removal.

However, I have since seen lots of other threads mentioning that it could be a ticking time-bomb to possible engine damage as I will now be running to rich or lean and in the long run it will cause problems.

What's the story here ? Should I look at putting back at least the front CATS ? Or perhaps install mini cats ? Lamdba foolers ?
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Old 11-10-2011, 08:45 AM
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Re: Remove CATS = Time Bomb ?

Quote:
Originally Posted by 0l1v3r View Post
I had all three CATS removed from my WJ (2003 4.7) a few months ago. The two front CATS were replaced with straight pipes and the rear CAT was replaced with a Free Flow silencer box. (We do not yet have emission laws in South Africa)

All O2 sensors were left where they were originally in the pipes.

I have not noticed a big difference in power or fuel consumption, but she sounds soooo much better ! The engine light never came on after the removal.

However, I have since seen lots of other threads mentioning that it could be a ticking time-bomb to possible engine damage as I will now be running to rich or lean and in the long run it will cause problems.

What's the story here ? Should I look at putting back at least the front CATS ? Or perhaps install mini cats ? Lamdba foolers ?
Unless there's something special about the Chrysler 4.7L engine, you can run catless and it's not a ticking time bomb. I've ran catless on my Mustang for YEARS. I used to have no cats on my Ranger. My buddy has a 01 WJ (4.0L engine) and he got his cats stolen at the Indy 500 about 8 years ago. All vehicles run fine w/out cats.

I do find it odd that you didn't throw any CEL. You should have front O2 sensors and rear O2 sensors. The front sensors (before the cats) are what adjust AF ratio. The rear sensors are just to tell you when your cats are bad and don't change AF ratio. When you remove cats the rear O2 sensors usually give an error and trip the CEL.
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Old 11-10-2011, 09:22 AM
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Re: Remove CATS = Time Bomb ?

I was also (pleasantly) surprised that I did not get the CEL. I know of another WJ 4.7 that also runs without the CEL and without all it's cats.

What worries/worried me is this from an WJ workshop manual:

Quote:
Two downstream sensors are used (1/2 and 2/2). The
downstream sensors are used to determine the correct
air-fuel ratio.
As the oxygen content changes at
the downstream sensor, the PCM calculates how
much air-fuel ratio change is required. The PCM
then looks at the upstream oxygen sensor voltage,
and changes fuel delivery until the upstream sensor
voltage changes enough to correct the downstream
sensor voltage (oxygen content).
The downstream oxygen sensors also provide an
input to determine mini-catalyst efficiency. Main catalytic
convertor efficiency is not calculated with this
package.
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Old 11-10-2011, 09:56 AM
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Re: Remove CATS = Time Bomb ?

I am not sure where you got that information, but it is my understanding that the upstream sensors control the air-fuel ratio. The downstream sensors are used to determine if the cats are working properly or not.
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Old 11-10-2011, 11:00 AM
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Re: Remove CATS = Time Bomb ?

Get it tuned u will enjoy the Jeep a lot better
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Old 11-10-2011, 12:18 PM
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What specifically should be tuned, ie. what should I ask the workshop to do ?
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Old 11-10-2011, 01:24 PM
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Re: Remove CATS = Time Bomb ?

It is fine, factory tune is rich
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Old 11-10-2011, 02:22 PM
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Re: Remove CATS = Time Bomb ?

Quote:
Originally Posted by 01grand View Post
I am not sure where you got that information, but it is my understanding that the upstream sensors control the air-fuel ratio. The downstream sensors are used to determine if the cats are working properly or not.
Yes this is correct. Factory sensors are narrowband though so not super accurate like a WB and PE is open loop on the 4.7 so no A/F monitoring or adjusting goes on at WOT. So, in theroy his vehicle could be running a little leaner or richer in some cases than commanded at WOT but unless he has something which dramatically changes the VE of the engine, LTs, Heads, Cams, etc it should be close to commanded at WOT.
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Old 11-10-2011, 02:30 PM
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Re: Remove CATS = Time Bomb ?

Dude, I have no idea what you just said ! Can you translate that to something more layman like ?
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Old 11-10-2011, 02:35 PM
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Re: Remove CATS = Time Bomb ?

See my post, he is agreeing with me
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Old 11-10-2011, 05:17 PM
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Re: Remove CATS = Time Bomb ?

Quote:
Originally Posted by 0l1v3r View Post
I was also (pleasantly) surprised that I did not get the CEL. I know of another WJ 4.7 that also runs without the CEL and without all it's cats.

What worries/worried me is this from an WJ workshop manual:
The only thing I would imagine is that "downstream" means after combustion and "upstream" means before combustion (aka, intake MAF). Upstream would be the input and downstream would be the exhaust. The two downstream sensors should be one on the left exhaust and one on the right exhaust.

That's how nearly all engines work now. The front exhaust O2 sensors monitor the exhaust. Based off their reading, it will compare the MAF reading and change fuel until the down exhaust O2 sensors rear correctly.
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Old 11-10-2011, 06:05 PM
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Re: Remove CATS = Time Bomb ?

Jeeps do not have maf!!!!!
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